In 3GPP, which is an organization that sets standards for third generation mobile communications systems, a study collectively termed as LTE (Long Term Evolution) has been conducted for achieving a drastic improvement of transmission speed and reduction of transmission delay in a radio access network (RAN); and formulation of standard specifications of the elemental technologies related to the study has been in progress.
As shown in FIG. 4, the radio access network (E-UTRAN: Evolved Universal Terrestrial RAN) in an LTE mobile communication system includes a mobile station UE (User Equipment) and a radio base station eNB (E-UTRAN Node B). This system is configured in such a way that the mobile station UE and the radio base station eNB communicate with each other via a radio link (RL).
Moreover, each of the mobile station UE and the radio base station eNB is configured to terminate an RLC (Radio Link Control) sublayer, a MAC (Medium Access Control) sublayer and a physical (PHY: Physical) layer.
In addition, a transmitting-side apparatus (mobile station UE or radio base station eNB) is configured to perform RLC processing, MAC processing and PHY processing sequentially for data to be transmitted, and then to transmit the data as radio signals from a radio unit.
Meanwhile, a receiving-side apparatus (mobile station UE or radio base station eNB) is configured to extract the transmitted data by performing PHY processing, MAC processing and RLC processing sequentially for the radio signals received by a radio unit.
Here, the data to be transmitted includes user data (U-plane data) generated by an application or the like used by the user, and control data (C-plane data) used in controlling the mobile communication system, such as RRC (Radio Resource Control) signaling and NAS (Non Access Stratum) signaling.
Moreover, this system is configured in such a way that RLC retransmission control processing is performed between the RLC sublayer of the transmitting-side apparatus and the RLC sublayer of the receiving-side apparatus, and that HARQ (Hybrid Automatic Repeat Request) retransmission control processing (MAC retransmission control processing) is performed between the MAC sublayer of the transmitting-side apparatus and the MAC sublayer of the receiving-side apparatus.
Here, in an IMT-2000 mobile communication system, a receiving-side apparatus is configured so that the MAC sublayer performs reordering processing for received RLC-PDUs (actually, MAC-PDUs to which the RLC-PDUs are mapped), and then transmits the RLC-PDUs to the RLC sublayer in the order of the sequence numbers, as shown in FIG. 1.
Accordingly, for RLC-data-PDUs (AMD-PDUs in the IMT-2000 mobile communication system; RLC-data-PDUs with sequence numbers #2 and #5) which have not yet been received but their subsequent RLC-data-PDU (RLC-data-PDU with sequence numbers #6) has been received when a STATUS-PDU generation trigger occurs as shown in FIG. 2, the RLC sublayer is configured to unconditionally determine that the packets are missing and to transmit a STATUS-PDU that requests retransmission of the RLC-data-PDUs with the sequence numbers #2 and #5.    Non-Patent Document 1: RLC Specification of IMT-2000: 3GPP TS 25.322 V6.9.0 (2006-09)    Non-Patent Document 2: LTE Stage 2 Specification: 3GPP TS 36.300 V8.0.0 (2007-03)
However, in the LTE mobile communication system, as shown in FIG. 3, a MAC sublayer is configured to transmit an RLC-PDU to an RLC sublayer without performing reordering processing for received RLC-PDUs in a receiving-side apparatus.
Thus, even though there exist RLC-data-PDUs (or RLC-data-Sub-PDUs) that have not yet been received by the RLC sublayer but their subsequent RLC-data-PDU (or RLC-data-Sub-PDU) has been received when a STATUS-PDU generation and transmission trigger occurs, it is not appropriate to unconditionally transmit a STATUS-PDU that requests retransmission of the RLC-data-PDUs (RLC-PDUs with the sequence numbers #2 and #5 in FIG. 2, for example). This is because there is a possibility that the RLC-data-PDU is in HARQ retransmission control processing in the MAC sublayer.
In this respect, the present invention has been made in view of the aforementioned problem. An object of the present invention is to provide a retransmission request transmitting method and a receiving-side apparatus in which an RLC sublayer can be prevented from transmitting a retransmission request for an RLC-data-PDU being in HARQ retransmission control processing in a MAC sublayer, in a case where the MAC sublayer does not perform reordering processing for received RLC-PDUs.
A first aspect of the present invention is summarized as a retransmission request transmitting method in which a predetermined sublayer of a receiving-side apparatus transmits a retransmission request for a packet transmitted from a predetermined sublayer of a transmitting-side apparatus, the method including the steps of: determining, at the predetermined sublayer of the receiving-side apparatus, whether or not a packet not received yet is under retransmission control processing in a lower sublayer of the predetermined sublayer of the receiving-side apparatus; and generating and transmitting, at the predetermined sublayer of the receiving-side apparatus, the retransmission request including only a packet which has neither been received yet nor is under the retransmission control processing in the lower sublayer, on the basis of the determination result, at a timing when the retransmission request is generated.
In the first aspect, the predetermined sublayer of the receiving-side apparatus cam manage the determination result as a state variable; and the predetermined sublayer of the receiving-side apparatus can, on the basis of the state variable, generate and transmit the retransmission request including only a packet which has neither been received yet nor is under the retransmission control processing in the lower sublayer.
A second aspect of the present invention is summarized as a receiving-side apparatus configured to transmit, from a predetermined sublayer, a retransmission request for a packet transmitted from a predetermined sublayer of a transmitting-side apparatus, wherein the predetermined sublayer is configured to determine whether or not a packet not received yet is under retransmission control processing performed in a lower sublayer of the predetermined sublayer, and the predetermined sublayer is configured to generate and transmit the retransmission request including only a packet which has neither been received yet nor is under the retransmission control processing in the lower sublayer, on the basis of the determination result, at a timing when the retransmission request is generated.
In the second aspect, the predetermined sublayer can be configured to manage the determination result as a state variable; and the predetermined sublayer can be configured to generate and transmit the retransmission request including only a packet which has neither been received yet nor is under the retransmission control processing in the lower sublayer, on the basis of the state variable.
As described above, according to the present invention, it is possible to provide a retransmission request transmitting method and a receiving-side apparatus in which an RLC sublayer can be prevented from transmitting a retransmission request for an RLC-data-PDU being in HARQ retransmission control processing in a MAC sublayer, in a case where the MAC sublayer does not perform reordering processing for received RLC-PDUs.